In the treatment of sewage, particularly involving single-family installations, the so-called "Septic systems" have been employed for many years, which systems employed solely anaerobic action in a suitable container and subsequent discharge of effluent into a suitable ground field.
More recently, various types of packaged waste treatment plants have been developed, which usually employ a modified activated sludge/extended aeration process, with the final plant effluent normally containing approximately 25 ppm BOD.sub.5 and approximately 50 ppm of suspended solids, chlorine, for example in tablet form, being utilized to provide final disinfection.
Systems employing granular-activated carbon are also known, and considerable data is at hand as to area and height of beds thereof, flows involved, as well as carbon reactivation requirements. For example, see U.S. Pat. No. 3,455,820. The use of carbon columns thus involves additional considerations. In addition to other problems as to size requirements etc., the carbon must be backwashed and eventually reactivated or replaced, the carbon usually being removed and heated in a furnace or kiln to a sufficient temperature to oxidize the adsorbed materials thereon, but insufficient to oxidize the carbon, for example 1500.degree.-1700.degree. F.
In addition, various procedures for "wet oxidative" reactivation of spent active carbon has also been devised utilizing air and water, the temperatures involved running from 125.degree. C. to 300.degree. C. or higher and may include relatively high pressures. See, for example, U.S. Pat. No. 3,150,105 and No. 3,386,922. It will be noted that operations of this type normally involve the removal of the carbon from the apparatus involved and reactivation in a suitable kiln, autoclave or the like, the operation normally taking at least a matter of hours. Operations of this type, requiring removal of the carbon from the apparatus involved, thus necessitate the use of standby units for operation when a spent unit is being reactivated, necessitating a greater number of units than actually required for the sewage treatment. Consequently, the use of carbon columns has been limited to installations that make the inclusion of a carbon column and means for reactivating the same both practical and feasible economically.
More recently the importance of the zeta potential (ZP), a long known principle of physical chemistry, has been recognized in connection with coagulation, particularly in connection with difficult raw-water colloids. The zeta potential is a measure of the electro-kinetic charge (in millivolts) that surrounds particulate matter. The charge on raw-water turbidity and suspended matter in domestic sewage is, on the average, predominately electro-negative and is strong enough to cause significant mutual repulsion, so that while coarse fractions, for example, ranging in particle diameter from 1 mm to 1 micron, may be relatively readily removed by conventional coagulation, fine colloidal fractions, for example, ranging from 1 micron to 10 Angstrom units, cannot. In such case the colloidal size prevents sedimentation and its electro-negative zeta potential (which may be in the range of -15 to -25 mv) prevents agglometaion.
In connection with the study of zeta potential reference is made to the following publications:
Zeta Potential: New Tool For Water Treatment, Thomas M. Riddick, Chemical Engineering, June 26, 1961, July 10, 1961 McGraw-Hill Publishing Company, Inc. PA0 Role of the Zeta Potential in Coagulation Involving Hydrous Oxides, Thomas M. Riddick, PA0 Tappi, The Journal of the Technical Association of The Pulp and Paper Industry, Volume 47, No. 1, January, 1964 PA0 Zeta-Meter Helps Filter-Rate Study, D. Lamoureux, Water and Pollution Control (Formerly Canadian Municipal Utilities), August, 1965
As will be apparent from the reference articles, the actual mechanics of the zeta potential and reduction in zeta potential of floc is not precisely factually known at the present time and explanations thus involve theoretical concepts. One such concept is described in the first mentioned article while the second mentioned article refers to the coating of each colloid with sufficient adsorbed hydrous oxides to bring its zeta potential to zero.
As a result, small systems have involved installations such as previously described, with the additional utilization of bacteria-enzymes etc. in an effort to achieve raid degredation. However, substantially all systems, particularly if the system is intended to bring the ultimate effluent within currently accepted standards, involve a considerable number of individual steps, requiring corresponding number of tanks, etc., with none of the systems actually being fully automatic, whereby no operating personnel are required. It will be appreciated that this problem is somewhat analagous to the electronic field wherein almost any electronic problem can be solved if size, number of components, complexity and costs are not of critical importance. Likewise, in water purification, almost any degree of purification can be achieved if the number of stages, vessels, filters, columns, multiple chemical treatments, size, cost and complexity are not controlling factors.
A very interesting and comprehensive study of waste water treatment concepts including a review of known types of systems (as of 3-1972) will be found in the treatise "Advanced Waste Water Treatment Concepts" by Dr. James E. Young, P.E.Research Consultant in Environmental Engineering, General Filter Company, Ames, Iowa, appearing in Bul. No. 7221, 3-72-2M-W, entitled "GFC Conservation for `better water`", published by General Filter Co.